We are past the times of wearing white shirts and khaki shorts/pants barefoot on the beach.
Wear What You Own
Shopping is not necessary for photos. What you already own if perfectly fine! What I recommend to Moms is to, typically find an outfit you love on yourself first, and then play off of that for the rest of your family members. Since you probably do most of the shopping anyway, you probably lean towards certain colors for your family.
Another way to think about your outfits is to choose colors that will look great in your house with your decor. So when you display your images they blend in well. Or you can go off a color palate, Pinterest is great for this. Find a swatch of 3-4 colors that go well together that you already have in your families wardrobe. Blue is a common color. Then a add a few pops of color like mustard yellow for fall or pops of teal for spring for example. You can do this with scarfs, cardigans in the fall, or in the spring with dress shoes or necklaces for example. or Have dad layer his sweater with a plaid undershirt and have the cuffs and collar pop out. I recommend not having too many patterns of the same color scheme. I also don't recommend having children wear the same shirt.
These are just a few ideas. If you are really concerned with what you have planned you are always welcomed to contact me and i can walk you through the process.